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Journal of Asian Ceramic Societies 3 (2015) 188–197

Contents lists available at ScienceDirect

Journal of Asian Ceramic Societies

HOSTED BY

j ourna l ho me pa ge: www.elsev ier .com/ locate / jascer

admium silicate nanopowders for radiation dosimetry application:uminescence and dielectric studies

.M. Manoharaa,b,∗∗, H. Nagabhushanac,∗, K. Thyagarajand, B. Daruka Prasadb,e,.C. Prashanthaf, S.C. Sharmag, B.M. Nagabhushanah

Department of Physics, Govt. First Grade College, Davangere 577004, IndiaJawaharlal Nehru Technological University, Ananthapura 515002, IndiaProf. C.N.R. Rao Centre for Advanced Materials, Tumkur University, Tumkur 572103, IndiaDepartment of Physics, JNTUA College of Engineering, Pulivendula 516390, IndiaDepartment of Physics, B.M.S. Institute of Technology, Bangalore 560064, IndiaDepartment of Physics, East West Institute of Technology, Bangalore 560091, IndiaChhattisgarh Swamy Vivekananda Technical University, North Park Avenue, Sector – 8, Bhilai, Chhattisgarh 490009, IndiaDepartment of Chemistry, M.S. Ramaiah Institute of Technology, Bangalore 560054, India

r t i c l e i n f o

rticle history:eceived 27 August 2014eceived in revised form 12 January 2015ccepted 6 February 2015vailable online 26 February 2015

eywords:eso-structured silicaanophosphorhermoluminescence

a b s t r a c t

Pure cadmium silicate (CdSiO3) nanophosphor was prepared by a low temperature solution combustiontechnique. In this technique, meso-structured silica was used as silica source. The prepared compoundswere well characterized by powder X-ray diffraction (PXRD), scanning electron microscopy, high resolu-tion transmission electron microscopy, Fourier transform infrared and UV–vis spectroscopic techniques.The PXRD peaks of as-formed sample are broad and amorphous in nature. The compound calcined at800 ◦C shows pure monoclinic phase, which is the lowest temperature reported so far to obtain in thisphase. The average crystallite size for phase pure compound was found to be ∼31 nm. The optical energyband gap of ∼5.6 eV was observed for the compound. Raman spectrum of the sample showed the allpossible states of vibrational motions of the prepared samples. The UV irradiated samples with different

ielectric dose and time with constant heating rate exhibit the thermoluminescence (TL) with a well resolved glowpeak at ∼160 ◦C. The variation of TL intensity with dosage time results that the material was found to bequite useful in radiation dosimetry. The frequency dependent dielectric constant of the prepared sampleexhibits high value at low frequency and vice versa.

© 2015 The Ceramic Society of Japan and the Korean Ceramic Society. Production and hosting byElsevier B.V. All rights reserved.

. Introduction

Phosphors with highly stable, good morphology and betterield were in great demand for energy saving applications such asisplay, lasers, scintillators, safety indicators and dosimetry [1,2].

n this regard, rare earth’s doped silicates based phosphors exhibitulti-color phosphorescence and are stable against acid, alkali

nd oxygen environments [3]. Various silicate hosts were well

∗

Corresponding author. Tel.: +91 9945954010; fax: +91 8162271924.∗∗ Corresponding author at: Prof. C.N.R. Rao Centre for Advanced Materials, Tumkurniversity, Tumkur 572103, India. Tel.: +91 9632552517.

E-mail addresses: bmm6627@gmail.com (B.M. Manohara),hushanvlc@gmail.com (H. Nagabhushana).

Peer review under responsibility of The Ceramic Society of Japan and the Koreaneramic Society.

ttp://dx.doi.org/10.1016/j.jascer.2015.02.003187-0764 © 2015 The Ceramic Society of Japan and the Korean Ceramic Society. Produc

studied by doping with rare earth and transition metal ions such asCdSiO3:In3+, CdSiO3:Mn2+, CdSiO3:Sm3+, CdSiO3:Tb3+, CaSiO3:Eu3+,Ba2SiO4:Eu2+, Sr2SiO4:Pr3+, Mg2SiO4:Tb3+, Zn2SiO4:Mn2+,Mg2SiO4:Eu3+, Mg2SiO4:Dy3+, and Sr2SiO4:Pr3+ [4–13]. Amongthe various silicates CdSiO3 as a host exhibits remarkable opticaland luminescent properties. Due to the presence of Cd2+ ions andstrong interaction between Si–O of SiO3 group, CdSiO3 showscombined nature of ionic and covalent bonding. The crystalstructure of CdSiO3 shows one dimensional chain of edge-sharingSiO4 tetrahedron helping in replacing the Cd site by transitionmetal ions. However in order to maintain the charge neutrality,the charge compensation of Cd2+ and O2− was tuned by rare earthions as a dopant. These dopants were responsible for the creation

of traps at appropriate depths, which stores the excitation energyand emit the light in the visible range after some time [14,15].

Thermoluminescence (TL) is a phenomenon of emission of lightcaused by thermal stimulation by the ionizing radiation on the

tion and hosting by Elsevier B.V. All rights reserved.

ian Ce

modTpmcstctoiwet((

2

2

qS83tTpiFa

2

nisirfptlontcw9

2

u(2bTteHi

the formation of cadmium silicate. Among the prepared silica, thesample calcined at 800 ◦C for 2 h shows better crystallinity andsingle monoclinic phase [22–24]. To the best of our knowledge,this is the best possible lowest temperature for the synthesis of

10 15 20 25 30 35 40 45 50 55 60

JCPDS NO.35 -081 0

Inte

nsity

(a.u

.)

(a)

(b)

(c)

(f)

(712

)

(413

)

( 020

)

(511

)(-20

3)(-

312)

(d)

(e)

(402

)(0

12)

(311

)(-

311)

(310

)(2

02)

(-11

1)(-

202)

(-40

1)

( 400

)(201

)

(001

)(2

00)

B.M. Manohara et al. / Journal of As

aterial induces electrons from the traps of the semiconductorsr insulators. A TL glow curve provides the information about theefect centers induced due to ionizing radiations in the material.L study mainly depends on particle size, type of dopant, mor-hology, crystallization, growth mechanism, local symmetry, hostatrix and synthesis methods. Further, TL finds wide range of appli-

ations in the field of archeology, radiation dosimetry and defecttudies [16,17]. Therefore, to improve the structural properties ofhe luminescent materials, the exothermic reaction based solutionombustion technique was developed [18]. The reported work inhis paper is the first time synthesis of CdSiO3 nanopowder usingxalyldihydrazide (ODH) as a fuel and meso-structured silica as sil-ca source during solution combustion. The prepared samples were

ell characterized by powder X-ray diffraction (PXRD), scanninglectron microscope (SEM), high resolution transmission elec-ron microscopy (HRTEM), Fourier transform infrared spectroscopyFTIR) and UV–vis spectroscopy (UV–vis). ThermoluminescenceTL), dielectric and ac conductivity studies were discussed in detail.

. Experimental

.1. Synthesis of meso-structured silica

Meso-structured silica was prepared by taking appropriateuantities of hexadecyltrimethyl ammonium bromide (CTAB,igma Aldrich), KOH and distilled water. The mixture was heated at0 ◦C for 30 min. After uniform mixing of solution for about 30 min,.0 mL of tetraethyl orthosilicate (TEOS, Sigma Aldrich) was addedo the mixture dropwise under fast stirring to obtain a suspension.he obtained suspension was kept at 80 ◦C for 2 h to complete therecipitation process. The decomposition of the prepared precip-

tate was controlled by allowing it to cool at room temperature.urther thoroughly washed with deionised water and dried for 12 ht 80 ◦C [19].

.2. Synthesis of CdSiO3 nanopowder

The materials used for synthesis of CdSiO3 were cadmiumitrate (Cd(NO3)2·4H2O) and freshly prepared meso-structured sil-

ca (Section 2.1) was used as the source of Cd and Si respectively. Thetoichiometric quantity of the redox mixture was taken in Petri dishn the ratio of 1:1 and dissolved in deionised water [20]. Then theequired amount of ODH was added to the mixture and stirred wellor 15–20 min using magnetic stirrer. The mixture was placed in areheated Muffle furnace maintained at 500 ± 10 ◦C. The reactionook place within few seconds by heating the redox mixture fol-owed by decomposition. During this process initially large amountf gases (usually CO2, H2O and N2) liberate followed by a sponta-eous ignition occurred and then the solution underwent flameype combustion with swelling. After combustion, the product wasooled and grinded well using mortar and pestle. The fine powderas calcined at various temperatures such as 600, 700, 800 and

00 ◦C for 2 h.

.3. Measurements

Powder X-ray diffraction (PXRD) analysis was performedsing Philips analytical X-ray diffractometer with CuK� radiation� = 1.5405 A) along with a nickel filter. The data were collected in� range from 10◦ to 60◦. Morphology of the sample was analyzedy using Hitachi table top scanning electron microscope (SEM –M 3000). Transmission electron microscopy (TEM), high resolu-

ion transmission electron microscopy (HRTEM) and selected-arealectron diffraction (SAED) pattern were done using JEOL 2100RTEM. Fourier transform infrared (FTIR) spectra were recorded

n absorption mode with Perkin Elmer spectrometer (Spectrum

ramic Societies 3 (2015) 188–197 189

1000) along with KBr pellets. UV–vis spectrum of the samplewas recorded with the Elico SL 159 spectrometer by dispersingthe powder in liquid paraffin. Raman spectra are recorded on aRaman Horiba Jobin yvon-labram-HR 800 Raman spectrometer inthe frequency range of 50–1200 cm−1. For TL studies, samples wereexposed to UV-source of wavelength 254 nm and power of 15 W.Samples were filled in the sample holder of squares with areaapproximately 1 cm2 by keeping the distance between the sourceand sample at constant distance of 1 cm where the intensity was0.028 W m−2. The samples were exposed in varied times such as5–40 min at room temperature (RT). After the desired exposure,the TL glow curves were recorded using Nucleonix TL reader con-sisting of a small metal planchet (72% Fe, 23% Al and 2% Cr orNichrome) heated directly using a temperature programmer. Dur-ing TL measurements, each time ∼30 mg of the samples were takenand heating rate was set to 5 ◦C s−1. Highly polished pellets with athin layer of silver paste on either side of the pellets (for ohmiccontacts) were used for dielectric measurements. Measurementswere carried out at room temperature (RT) using LCR meter modelHIOKI 3532-50 LCR HiTESTER version 2.3, in the frequency range of50 Hz–5 MHz.

3. Results and discussion

3.1. Investigations from PXRD

Fig. 1 shows the PXRD patterns of mesoporous silica (Fig. 1(a);JCPDS card No. 47-0715), CdO (Fig. 1(b); JCPDS card No. 78-0653)and CdSiO3 (Fig. 1(c)–(f)). The diffraction peaks of CdSiO3 werewell matched with the JCPDS card No. 35-0810 [21] confirming

2θ (Deg ree )

Fig. 1. PXRD of mesoporous silica, CdO and CdSiO3: (a) mesoporous silica, (b) asformed sample contains CdO and amorphous silica. Further, samples were calcinedat (c) 600 ◦C, (d) 700 ◦C, (e) 800 ◦C and (f) 900 ◦C for 2 h.

1 sian Ceramic Societies 3 (2015) 188–197

Cs[

d

wnuT∼ttsm(

ˇ

w‘a

0.8 1.0 1.2 1.4 1.6 1.80.00 0

0.00 2

0.00 4

0.006

0.00 8

0.01 0

ββcos

θθ

90 B.M. Manohara et al. / Journal of A

dSiO3 so far observed in the literature. The average crystalliteize was estimated by employing the Debye-Scherrer’s formula25,26].

= k�

cos �(1)

here is the full width at half maximum (FWHM) of the promi-ent diffraction peaks, ‘�’ is the wavelength of X-ray (� = 1.5405 A)sed, ‘�’ is the Bragg’s angle and ‘k’ is the Scherrer’s constant.he average crystallite size of the CdSiO3 sample was found to be31 nm for the samples calcined at 800 ◦C for 2 h. It is known that

he FWHM can be expressed as a linear combination of the con-ribution from the lattice strain and crystalline size [27]. Further,train present in the CdSiO3 nanopowder prepared by above-entioned method was estimated using the Williamson–Hall

W-H) equation.

cos � = k�

D+ 4ε sin � (2)

here is the FWHM (in radians), ‘�’ is the Bragg angle of the peak,�’ is the wavelength of X-ray used, ‘D’ is the effective particle sizend ‘ε’ is the effective strain [28]. The effectiveparticle size for which

Fig. 3. SEM images of CdSiO3 nanopowder: (a) CdO and amorphous silica combin

4sinθθ

Fig. 2. Williamson–Hall plots of CdSiO3 nanopowder calcined at 800 ◦C for 2 h.

the strain has been taken into account can be estimated from theextrapolation of the plot as shown in Fig. 2. The average crystallitesize estimated from Scherrer’s method and W-H plots was wellmatched with one another.

ation (b–f) calcined at (b) 600 ◦C, (c) 700 ◦C, (d) 800 ◦C and (e) 900 ◦C for 2 h.

B.M. Manohara et al. / Journal of Asian Ceramic Societies 3 (2015) 188–197 191

(d) ED

3

SosdpeaatSTXFfie[

3

i4(wswwbdtf

The optical energy gap (Eg) of CdSiO3 nanopowder calcined at800 ◦C for 2 h was calculated using Tauc relation [33]. The energy

5001000150020002500300035004000

343

875

(e)

(d)

(c)

(b)

(a)

1114

% T

rans

mit

tanc

e (a

.u)

464

Fig. 4. (a) HRTEM image. (b) TEM image. (c) SAED.

.2. Morphological analysis

Transmission and scanning electron microscopes (TEM andEM) together provide an important tool for the characterizationf nano and surface morphologies of the materials. SEM analysishown in Fig. 3 reveals that the morphology of CdSiO3 nanopow-ers was porous and agglomerated with polycrystalline nature. Theores and voids can be attributed to the large amount of gasesscaping out of the reaction mixture during combustion. HRTEMnd TEM images of CdSiO3 nanopowder were shown in Fig. 4(a)nd (b) respectively. The sample consists of irregular shaped par-icles with an average particle size of ∼30 nm. Fig. 4(c) shows theAED pattern of CdSiO3 nanopowder having polycrystalline nature.he possible elements present were studied by energy dispersive-ray analysis (EDAX) shown in Fig. 4(d) and table as a inset ofig. 4(d) shows quantity of element present in the sample con-rming the presence of only Cd, Cu, Si and O elements. The Culement identified was due to copper grid used as a base material29,30].

.3. Fourier transform infrared (FTIR) spectroscopy

In order to investigate the nature of the chemical bonds formedn the prepared sample, FTIR spectra were recorded in the range of000–400 cm−1 using Perkin Elmer Spectrum 65 with KBr pelletsFig. 5). The spectra showing the broad band from 875 to 1114 cm−1

as due to asymmetric stretching vibration of Si O Si bond andtretching vibrations of terminal Si O bonds. The peaks at 468 cm−1

ere the characteristic stretching vibrations of Si O Si bridges. Aeak absorption peak at 2397 cm−1 indicating the presence of C O

ond in the structure, may be due to adsorbed CO2 in the sampleuring FTIR measurements [31,32]. The sharp peak correspondingo ∼680 cm−1 can be ascribed to Si O bond, which exists in theorm of SiO3. The absorption at around 3490 cm−1 indicates the

X of CdSiO3 nanopowder calcined at 800 ◦C for 2 h.

presence of hydroxyl groups (surface adsorbed), which is probablydue to the fact that the spectra were not recorded in situ whichleads to absorption of water from the atmosphere.

3.4. UV–vis spectra investigations

Wavenumber (cm-1)

Fig. 5. FTIR of CdSiO3 nanopowder: (a) as formed and calcined at (b) 600 ◦C, (c)700 ◦C, (d) 800 ◦C and (e) 900 ◦C for 2 h.

192 B.M. Manohara et al. / Journal of Asian Ceramic Societies 3 (2015) 188–197

54321

0.0

2.0x10-11

( ααhv

)2(e

V cm

-2)2

E=hνν (eV)Eg = 5.6 ev

120010008006004002000.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

Abs

orba

nce(

a.u)

Wavelenth(nm)

280 nm

FU

ga

(

w1dfoc(tf

3

topi[ew1r

Table 1Raman shifts and their respective matching modes with identical symmetry ofCdSiO3.

Raman shift (cm−1) Irreducible representation [36]

130.7 Au

273.0 B2g

313.8 Ag

402.7 B2g

487.7 Ag

633.0 B3g

703.0 B3g

856.4 B3g

966.9 B3g

sity with UV dose and a strong peak was observed at ∼110–160 ◦C.The main process of the dissipation of energy absorbed by a mate-rial with self-trapped exciton is due to annihilation of self-trapped

ig. 6. Energy band gap of CdSiO3 nanopowder calcined at 800 ◦C for 2 h (inset:V–vis absorption spectrum of CdSiO3 nanopowder).

ap (Eg) has been evaluated for CdSiO3 nanopowder by fittingbsorption data to the direct transition equation

˛hc/�) = A(

hc

�− Eg

)n

(3)

here � is the wavelength, A is the constant and n can have values/2, 3/2, 2 and 3 depending on the mode of inter-band transition, i.e.irect allowed and direct forbidden, indirect allowed and indirectorbidden transitions respectively. Plotting (˛hc/�)2 as a functionf photon energy (hc/�) and extrapolating the linear portion of theurve at zero absorption gives the value of the direct band gap (Eg)Fig. 6). The inset of Fig. 6 shows the UV–vis absorption spectrumaken in the range of 200–1100 nm. The estimated value of Eg isound to be ∼5.6 eV.

.5. Raman spectrum of pure CdSiO3

The Raman spectrum is widely used to study vibrational, rota-ional, and other low-frequency modes in a system. The interactionf light with atomic vibrations results in the energy of incidenthotons being shifted up or down, the energy shift being depend-

ng on the spatial derivatives of the macroscopic polarization34,35]. The Raman spectrum for the sample indicates the pres-

nce of prominent and highest vibrational band at 966.7 cm−1 alongith two antisymmetric stretching modes appearing at 1006.2 and

036 cm−1 (Fig. 7). The peak at 1006.3 cm−1 is due to the symmet-ic stretching mode of the SiO6 octahedral group; the two lower

120010008006004002000

500

1000

1500

2000

2500

3000

487.

76

289.

6727

3 .64

156.

15

130.

72

107.

77

75.3

213 .

65

313.

81

567.

79402.

74

633.

02

703.

33

856.

38

966.

96

1 006

.21

Ram

an in

tens

ity

(a.u

)

Wave number (cm-1)

1036

Fig. 7. Raman spectrum of CdSiO3 in the range 50–1200 cm−1.

1006.0 B3g

1036.0 B3g

frequency modes 633.02 and 856.38 cm−1 are likely to be asso-ciated with motion of the cadmium ion. Bands below 350 cm−1

are due to external modes and are difficult to be assigned becauseof mixing. At 487 cm−1, the Ag mode corresponds to the scissorsmovement of Si–O–Si groups along the c axis, while the peak at273 and 130.7 cm−1 are due to an Au and B3g mode related with thebending of O–Si–O groups within the ab plane and the simultaneousmovement of Cd ions along the b axis. Table 1 lists the band loca-tions for the major Raman bands and shoulders along with otherpossible modes.

3.6. Thermoluminescence (TL) studies

TL behavior of UV rayed sample was studied in the range of4.7–38 Gy dose at RT. The dose was calculated by considering thedimensions of the sample holder, the distance of the sample fromthe UV source, density of the sample filled in the sample holderand the standard parameters like wavelength, power and num-ber of photons emission per second of the used UV bulb. TL glowcurves of CdSiO3 nanopowder and the variations of TL intensityas a function of UV dose (4.7–38 Gy) were shown in Fig. 8 andFig. 9(a), respectively. TL glow curve shows the increase in inten-

0

50

100

150

200

250

0

1x104

2x104

3x104

4x104

5x104

510

1520

2530

3540

TL

Inte

nsit

y(a.

u)

Temperature ( 0C) UV Exposure tim

e (min)

Fig. 8. TL glow curves of UV irradiated CdSiO3 nanopowder.

B.M. Manohara et al. / Journal of Asian Ceramic Societies 3 (2015) 188–197 193

F(e

aah

afohfatlcUiiwist

Tdses

ig. 9. (a) Variation of TL intensity as a function of UV irradiation dose (5–40 min).b) Effect of fading with number of days in pure CdSiO3 nanopowder (25 min UVxpose time).

nd impurity-trapped excitons. The observed TL peaks may bettributed to recombination of trapped electrons with differentoles [37–41].

Fading is the unintentional loss of the TL signal which leads ton underestimation of the absorbed dose. Thermal fading initiatesrom the fact that even at room temperature there is a cause byptical stimulation. In general, high-sensitivity materials should beandled carefully and stored in opaque containers to prevent fading

rom light exposure. Other types of fading, which are not temper-ture dependent, are caused by quantum mechanical tunneling ofhe trapped charge to recombination sites and transitions betweenocalized states, i.e. transitions that do not take place via the delo-alized bands. To study the fading effect, the pure CdSiO3 was givenV expose for about 25 min. The TL signal was recorded at different

ntervals of time for nearly 30 days. Fig. 9(b) shows the plot of TLntensity versus the number of days after irradiation. Strong fading

as observed after 15 days with the TL signal losing around 62% ofts initial value. Subsequently, the signal decayed slowly and finallytabilized after 20 days. The 41% remnant TL signal is high enougho be considered for dosimetric applications [21].

TL glow of the nanopowder might be due to the surface defects.he glow peaks occurred indicate the creation of trapped carriers

uring irradiation. In nanopowder, most of the ions were at theurface, leading to unsaturated coordinates or easy excitation oflectrons or holes. Due to this, the charge carriers are trapped aturface states located in the forbidden gap. During heating process

Fig. 10. Glow curve deconvolution of CdSiO3 nanopowder (UV dose: 30 min).

the recombination of de-trapped electrons and holes emits light.Increase in TL intensity with UV dose is because of more and moretraps were getting filled with the increase of absorbed dose and onheating recombination of more and more electrons with holes willrelease more intense light [42,43].

The dosimetric properties of a material depend mainly on thekinetic parameters responsible for TL. The parameters are acti-vation energy or trap depth (E), the frequency factor (s) and theorder of kinetics (b). These parameters will give information aboutthe stability of the traps. If the activation energy is low, then theglow peak occurs at a relatively lower temperature and the corre-sponding trap is unstable. If it is high, then the trap is relativelystable. The order of kinetics reveals about whether the trappedcharge carriers will be retrapped on heating or not. There are sev-eral methods present in the literature for the determination of theseparameters [44–47]. In the present study the above mentionedparameters were determined by three different standard meth-ods namely Luschik, Halperin–Braner and Chen’s method. Glowcurve deconvolution of CdSiO3 nanopowder exposed to UV dosewas used for the estimation of kinetic parameters (Table 2). Fig. 10shows glow curve deconvolution of CdSiO3 nanopowder (UV dose:30 min).

The empirical formulae for estimating trapping parameters byChen’s peak shape method [40] are given by

E˛ = c˛

(kT2

m˛

)− b˛(2kTm)

where with

� = Tm − T1, ı = T2 − Tm, ω = T2 − T1

The order of kinetics (b) or form factor (symmetry factor) ‘�g’ isgiven by

�g = T2 − Tm

T2 − T1(4)

= �, ı, ω

where T1 and T2 were calculated, they are the temperatures cor-responding to the half of the maximum intensities on either sideof the glow peak maximum temperature (Tm). The nature of thekinetics was found by the form factor. Theoretically, the value of

geometrical form factor (�g) is ∼0.42, for first order kinetics and∼0.52 for second order kinetics. The ‘�g’ is found to be practicallyindependent of the activation energy ‘E’ and strongly depends onthe order of kinetics [41].

194 B.M. Manohara et al. / Journal of Asian Ceramic Societies 3 (2015) 188–197

Table 2Estimated kinetic parameters using UV irradiated (5–40 min) CdSiO3 nanopowder.

UV-dose (Gy)exposed to thesample fordifferent times

Peak Tm (◦C) Balarinparameter(�)

Order ofkinetics, b(�g)

Activation energy (eV) Frequencyfactor, s (s−1)

Lushchik method Halperin–Braner method Chen’s method

∼4.71 93.91 0.95 2(0.51) 0.89 0.65 0.72 9.66E+092 131.15 1.09 2(0.48) 0.88 0.57 0.59 1.64E+073 175.58 0.98 2(0.51) 1.33 0.95 1.05 8.41E+11

∼91 95.91 1.06 2(0.49) 1.71 1.12 1.25 2.4E+172 131.95 1.04 2(0.49) 0.67 0.45 0.46 3.15E+053 174.39 1.05 2(0.49) 2.00 1.34 1.49 9.43E+16

∼141 94.93 0.97 2(0.51) 1.72 1.25 1.43 9.70E+192 118.46 0.95 2(0.51) 0.69 0.51 0.55 8.47E+063 175.77 1.03 2(0.49) 1.12 0.76 0.82 1.56E+09

∼191 102.2 0.97 2(0.51) 0.91 0.66 0.73 6.43E+092 135.25 1.00 2(0.50) 1.97 1.38 1.56 4.09E+193 164.74 0.98 2(0.4951) 0.94 0.67 0.73 1.96E+08

∼241 94.27 1.00 2(0.50) 1.93 1.35 1.54 3.80E+212 117.6 0.99 2(0.50) 0.75 0.26 0.55 1.05E+073 173.86 1.00 2(0.50) 1.18 0.83 0.90 1.45E+10

∼281 104.18 1.03 2(0.49) 0.89 0.61 0.65 4.83E+082 152.11 1.03 2(0.49) 1.01 0.69 0.74 4.49E+083 184.77 1.08 2(0.48) 1.62 1.05 1.14 4.28E+12

∼331 104.12 1.03 2(0.49) 0.87 0.59 0.63 2.46E+082 152.11 1.03 2(0.49) 1.01 0.69 0.74 4.49E+083 184.77 1.02 2(0.49) 1.49 1.02 1.12 2.31E+12

1.730.662.12

poi

E

gt

E

w

E

a

w

ps

3

i

where ε′ and ε′′ are the real and imaginary parts of the complexdielectric permittivity.

The variation of frequency dependent dielectric constant atroom temperature is as shown in Figs. 11 and 12. It has been

1 2 3 4 5 6300

400

500

600

εε′′′′

εε′′

0

500

1000

∼381 96.59 1.07 2(0.48)

2 131.15 1.00 2(0.50)

3 174.65 1.05 2(0.49)

In the Luschik method [48], the descending part of the gloweak was used where the area of the half peak, resembled the areaf the triangle having identical height and half width. The equations given by

˛ = 2

{kT2

m

ı

}(5)

In Halperin and Braner [49] method, the ascending part of thelow peak whose area was assumed to be equal to the area of theriangle is given by

˛ = 2

{kT2

m�

}(1 − 3) (6)

here

= 2{

kTm

E

}

In modified Chen’s method activation energy is given by [46]

= 3.52

{kT2

mω − 1

}(7)

The equation used for the calculation of frequency factor (s)ccording to Randall and Wilkinson [50] is given by

ˇE

kT2m

= s exp{ −E

kTm

}Zm (8)

here k is the Boltzmann constant and Zm = 1 + (b − 1)m.All the calculated parameters were tabulated in Table 2. The

resence of deep traps in CdSiO3 nanopowder suggests that theample can be used as a low dose UV radiation dosimeter.

.7. Dielectric interactions

Few dielectric materials show transient phenomenon on heat-ng followed by irradiation. These phenomena display the same

1.13 1.25 2.11E+17 0.46 0.48 5.06E+05 1.41 1.57 7.53E+17

pattern on behavior for TL, thermally stimulated conductivity (TSC)and exoelectron emission (TSE). These dielectric materials can beused for radiation dosimetry applications. The prepared samplesshow the insulating behavior based on the energy band gap cal-culation; hence to check the dielectric behavior the impedancespectroscopy was investigated [51]. Further, this study provides theSiO3 which can be regarded as probes of the crystal field strengthand symmetry in sites occupied by Cd2+ ions. The complex dielectricpermittivity of the CdSiO3 is generally

ε∗ = ε′ + iε′′ (9)

10 10 10 10 10 10Frequency (Hz)

Fig. 11. Variation of real and complex permittivity with frequency at room temper-ature.

B.M. Manohara et al. / Journal of Asian Ceramic Societies 3 (2015) 188–197 195

1 0 2 1 0 3 1 0 4 1 0 5 1 0 6

0 .0 0

4 .7 0 x 1 0 -6

9 .4 0 x 1 0 -6

1 .4 1 x 1 0 -5

0 .0 0

7 .8 0 x 1 0 -4

1 .5 6 x 1 0 -3

2 .3 4 x 1 0 -3

0 .0 0

2 .8 0 x 1 0 -4

5 .6 0 x 1 0 -4

8 .4 0 x 1 0 -4

0 .0 0

6 .2 0 x 1 0 -1

1 .2 4 x 1 0 0

1 .8 6 x 1 0 0

e q u

σσ acM

′′M

′′′′ta

n (δδ

)

tivity

owfitfhfqd

taidfp

a

t

Ffdfqoi

F r

Fig. 12. Variation of tan ı, ac conduc

bserved that all the samples exhibit the dielectric dispersionhere dielectric constant decreases as the frequency increases

rom 1 Hz to 1 MHz. The decrease in dielectric constant withncreasing frequency reaches a constant value and accounts forhe fact that beyond a certain frequency, electron hopping cannotollow the alternating field [52]. In view of the fact that mobility ofoles is smaller than electrons, the contribution to the polarization

rom holes is smaller and decreases more rapidly even at lower fre-uencies than from the later. As a result, the net polarization andielectric constant decrease.

The values of dielectric constant at lower frequency were foundo be about 600–1000 for 100 Hz. The variation in ε′ was alsottributed to the fact that at low frequency regime, the dipolar,nterfacial or the surface polarization plays a leading role inetermining the dielectric properties of silicates [53]. The higherrequency dielectric constant was attributed to ionic and electronicolarizations that are independent of frequency.

The dielectric loss factor or the dissipation factor is representeds

an ı = ε′

ε′′ (10)

ig. 12 shows the variation of dielectric loss as a function ofrequency for the prepared samples. There is a normal trend ofielectric loss without any peaking behavior. It may be due to the

act that the resonance matching may be beyond the analyzed fre-uency range [54]. Hence there is no power loss due to the transferf energy from applied field to the oscillating ions within the stud-ed frequency range.

e n c y (H z )

and elastic moduli with frequency.

3.8. A.C. conductivity

In order to understand the conduction mechanism, the ac con-ductivity can be evaluated from the dielectric loss and dielectricpermittivity as

ac = ε′ε0ω tan ı (11)

The variation of ac conductivity of the sample as a function offrequency is as shown in Fig. 12. The ac conductivity graduallyincreases as the frequency of applied field increases. The variationof ac conductivity could be explained in terms of two frequencyregions: low frequency and high frequency regions. In low fre-quency region, grain boundaries are found to be more active sothe hopping probability of charge carriers is less whereas, in highfrequency region conducting grains are more active promoting thehopping of charge carriers. Probability of charge carriers is less inlow frequency region, whereas in high frequency region conductinggrains are more active in promoting the hopping of charge carriers.The total conductivity of silicates is:

(ω, T) = dc(T) + ac(ω, T) (12)

where dc is the dc conductivity due to band conduction and ac isthe ac conductivity due to electron hopping between the Cd2+ andSiO3 sites. Fig. 12 shows the variation of elastic moduli (M′ and M′′)with frequency supporting the trend of tan(ı) variation.

Fig. 13 shows the variations of impedance, resistance and resis-

tivity with frequency. All the terms decreases in their trend withfrequency was due to the presence of increased charge carriers likeelectrons, holes and polarons. The Nyquist plot (Fig. 14) for all thecompositions shows one overlaid semicircle showing the presence

196 B.M. Manohara et al. / Journal of Asian Ceramic Societies 3 (2015) 188–197

102 103 104 105 106

0.00

2.80 x106

5.60 x106

8.40 x106

0.00

3.20 x106

6.40 x106

9.60 x106

0.00

9.90x106

1.98x107

2.97 x107

0.00

2.50x106

5.00x106

7.50x106

-4.50 x106

-3.00 x106

-1.50x106

0.00

Fre

ZR

ρρZ

′′′′Z

′′

e and

otat

Fig. 13. Variation of impedanc

f single phase with different electrical properties. The higher resis-ance is attributed to the grain resistance while the lower resistancet lower frequency is attributed to the accumulation of layer resis-ance. Based on the dielectric behavior and frequency dependent

0 1x106 2x106 3x106 4x106 5x106 6x106 7x106 8x106 9x1060

-1x1 06

-2x1 06

-3x1 06

-4x1 06

-5x1 06

Z′′ (

Ω)

Z′ (Ω)

Fig. 14. The complex impedance as a Nyquist plot for CdSiO3 nanopowder.

quency (Hz)

resistance with the frequency.

resistance, the prepared materials are suitable for using it in thelow dose radiation dosimeters.

4. Conclusion

For the first time CdSiO3 nanopowder was successfully syn-thesized by self sustainable propellant chemistry technique usingmeso-structured silica as a silica source. PXRD analysis confirmsthe monoclinic phase and is formed at low calcined temperature of800 ◦C for 2 h. SEM, TEM and HRTEM images show that the powderwas highly porous in nature with lots of voids, foamy and agglom-eration. The UV–vis spectra give the energy band gap of ∼5.6 eV.Single glow peak was seen at 160 ◦C and TL intensity increases lin-early with UV dose. Raman spectrum of the sample showed theall possible states of vibrational motions of the prepared samples.This analogy shows important applications in radiation dosime-try. The dielectric dispersion as a function of frequency shows thenon-peaking behavior. Due to increased charge carriers, higher con-ductivity was observed at higher frequency. The CdSiO3 systemshows the high resistance attributed to both grain and grain bound-ary contributions respectively. The single semicircle of Nyquist plot

supports for the single phase of the compound matches with thePXRD results. Hence a simple method of preparation of CdSiO3may be the better material for luminescent and low dose radiationdosimeters.

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B.M. Manohara et al. / Journal of As

cknowledgements

The author B.M. Manohara is grateful to the Principal andhe Head of the Department of Physics, Govt. First Grade Col-ege, Davangere, for his constant support and encouragement. Theuthor BMM acknowledges UGC (Project No. MRP/12TH PLAN/14-5/KAD008), New Delhi for sanction of the Project and extendspecial gratitude to Prof. C.N.R. Rao Centre for Advanced Materi-ls, Tumkur University, Tumkur 572103, India for extending labacilities.

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